Generally, photosensitive film used for making a printed circuit of a printed circuit board is manufactured through the steps of applying a photosensitive resin compound on a polyester film by a proper thickness, drying it at a predetermined temperature, and laminating a polyethylene film thereon. Here, the photosensitive resin composition comprises a polymeric binder as a binding carrier and a compound having at least one terminal ethylenically unsaturated group, i.e., a photopolymerizable monomer mixed with a photoinitiator and a solvent as main components.
An apparatus for manufacturing photosensitive film is shown in FIG. 1. As shown in FIG. 1, the apparatus comprises a photosensitive resin supplying section 1 which makes a photosensitive resin compound and supplies a proper amount of the photosensitive resin compound, a polyester film supplying section 2 for supplying a polyester film on which the photosensitive resin compound supplied from the photosensitive resin supplying section 1 is applied, a drying section 3 for drying the photosensitive resin compound applied on a base layer of a photosensitive film 6, a polyethylene film supplying section 4 which supplies a polyethylene film in such a manner that a surface layer of the photosensitive film 6 can be laminated on a photosensitive layer of the photosensitive film 6 which has been dried by the drying section 3, and a winding section 7 for winding the photosensitive film 6 having the base layer, the surface layer, and the photosensitive layer interposed therebetween.
The photosensitive film 6 that has been wound by the winding section 7 consists of the photosensitive layer 6a, the base layer 6b formed on one side of the photosensitive layer 6a, and the surface layer 6c formed on the other side of the photosensitive layer 6a. In addition, as shown in FIG. 2, the photosensitive film 6 which is cut in a predetermined width and length is wound around a cylindrical core 8.
The photosensitive film 6 is classified into an alkaline development type in which a non-exposed portion is removed by an alkaline aqueous, and a solvent development type in which a non-exposed portion is removed by an organic solvent. In the alkaline development type photosensitive film, a predetermined circuit pattern is obtained by the steps of separating the surface layer 6c from the photosensitive film 6, heating and pressing the photosensitive layer 6a in such a manner that the photosensitive layer 6a can make contact with the board while maintaining the base layer 6b to be coated on the photosensitive layer 6a, placing a mask film having a predetermined pattern on the base layer 6b, and exposing the photosensitive film 6 to ultraviolet rays.
However, the above mentioned photosensitive film 6, which is formed by stacking the photosensitive layer 6a, the base layer 6b and the surface layer 6c with each other, has a semi-solid state. Accordingly, if the photosensitive film 6 which is being wound around a core is subjected to a high tension, a pressure applied to the photosensitive layer 6a increases so that the photosensitive resin may be deformed. This kind of deformation may cause both edges of the wound photosensitive film 6 to be fused which is called "edge fusion phenomenon", thereby making the photosensitive film 6 non-available. On the contrary, if a low tension is applied to the photosensitive film 6 which is being wound around the core, some of the photosensitive film 6 that has been wound around the core deviates from its initial wound position, so the winding shape of the photosensitive film 6 is deformed which is called "telescope phenomenon", thereby resulting that the photosensitive film 6 is no more available to other processes in which the photosensitive film should be used.
In addition, in case that the size of the photosensitive film 6 is not suitable to the standard size (i.e., width of 300 to 500 mm, length of 100 to 200 mm), in other words, when the photosensitive film 6 has a width less than 300 mm and a length more than 300 m, the pressure applied to each layer of the photosensitive film wound around the cylindrical core is in inverse proportion to both a diameter and a width of each layer, and is in proportion to a winding tension of each layer, so the above mentioned "edge fusion phenomenon" or "telescope phenomenon" happens to be more extreme happened.
That is, as the length of the photosensitive film increases or as the width of the photosensitive film reduces, the higher tension should be applied to the photosensitive film to be wound in order to maintain the winding shape of the photosensitive film. However, if the tension applied to the photosensitive film becomes higher, the pressure applied to the photosensitive layer increases so that the semi-solid photosensitive resin may be more extremely deformed.